A Michigan woman on a snowmobiling trip captured video of a bizarre phenomenon: a disc of ice slowly rotating on the surface of a river.
Karla S. Dahms posted a video to Facebook showing the strange rotating ice circle she spotted in the Muskegon River, near the city of Houghton Lake.
Dahms said she had never seen anything like the ice disc in the river before.
Researchers determined the ice discs occur when cold air comes in contact with an eddy in the river and the ice forms into a circle, which rotates due to the current it creates by slowly melting.
In a paper published in Physical Review E in July last year, scientists from the Université de Liège in Belgium used magnets to simulate the conditions in these frozen rivers.
Using petri dishes, they found blocks of ice would start to rotate even when no current was present, due to the melting of the ice.
This means the spin is caused by melting ice, not the eddies in the water itself.